Java tutorial
package net.yasion.common.core.bean.wrapper; /* * Copyright 2002-2014 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ import java.beans.BeanInfo; import java.beans.IntrospectionException; import java.beans.Introspector; import java.beans.PropertyDescriptor; import java.util.Collections; import java.util.Iterator; import java.util.LinkedHashMap; import java.util.List; import java.util.Map; import java.util.Set; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.ConcurrentMap; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.beans.BeanInfoFactory; import org.springframework.beans.BeansException; import org.springframework.beans.FatalBeanException; import org.springframework.core.SpringProperties; import org.springframework.core.convert.TypeDescriptor; import org.springframework.core.io.support.SpringFactoriesLoader; import org.springframework.util.ClassUtils; import org.springframework.util.ConcurrentReferenceHashMap; import org.springframework.util.StringUtils; /** * Internal class that caches JavaBeans {@link java.beans.PropertyDescriptor} information for a Java class. Not intended for direct use by application code. * * <p> * Necessary for own caching of descriptors within the application's ClassLoader, rather than rely on the JDK's system-wide BeanInfo cache (in order to avoid leaks on ClassLoader shutdown). * * <p> * Information is cached statically, so we don't need to create new objects of this class for every JavaBean we manipulate. Hence, this class implements the factory design pattern, using a private constructor and a static {@link #forClass(Class)} factory method to obtain * instances. * * <p> * Note that for caching to work effectively, some preconditions need to be met: Prefer an arrangement where the Spring jars live in the same ClassLoader as the application classes, which allows for clean caching along with the application's lifecycle in any case. For a web * application, consider declaring a local {@link org.springframework.web.util.IntrospectorCleanupListener} in {@code web.xml} in case of a multi-ClassLoader layout, which will allow for effective caching as well. * * <p> * In case of a non-clean ClassLoader arrangement without a cleanup listener having been set up, this class will fall back to a weak-reference-based caching model that recreates much-requested entries every time the garbage collector removed them. In such a scenario, consider the * {@link #IGNORE_BEANINFO_PROPERTY_NAME} system property. * * @author Rod Johnson * @author Juergen Hoeller * @since 05 May 2001 * @see #acceptClassLoader(ClassLoader) * @see #clearClassLoader(ClassLoader) * @see #forClass(Class) */ public class CachedIntrospectionResults { /** * System property that instructs Spring to use the {@link Introspector#IGNORE_ALL_BEANINFO} mode when calling the JavaBeans {@link Introspector}: "spring.beaninfo.ignore", with a value of "true" skipping the search for {@code BeanInfo} classes (typically for scenarios where * no such classes are being defined for beans in the application in the first place). * <p> * The default is "false", considering all {@code BeanInfo} metadata classes, like for standard {@link Introspector#getBeanInfo(Class)} calls. Consider switching this flag to "true" if you experience repeated ClassLoader access for non-existing {@code BeanInfo} classes, in * case such access is expensive on startup or on lazy loading. * <p> * Note that such an effect may also indicate a scenario where caching doesn't work effectively: Prefer an arrangement where the Spring jars live in the same ClassLoader as the application classes, which allows for clean caching along with the application's lifecycle in any * case. For a web application, consider declaring a local {@link org.springframework.web.util.IntrospectorCleanupListener} in {@code web.xml} in case of a multi-ClassLoader layout, which will allow for effective caching as well. * * @see Introspector#getBeanInfo(Class, int) */ public static final String IGNORE_BEANINFO_PROPERTY_NAME = "spring.beaninfo.ignore"; private static final boolean shouldIntrospectorIgnoreBeaninfoClasses = SpringProperties .getFlag(IGNORE_BEANINFO_PROPERTY_NAME); /** Stores the BeanInfoFactory instances */ private static List<BeanInfoFactory> beanInfoFactories = SpringFactoriesLoader .loadFactories(BeanInfoFactory.class, CachedIntrospectionResults.class.getClassLoader()); private static final Log logger = LogFactory.getLog(CachedIntrospectionResults.class); /** * Set of ClassLoaders that this CachedIntrospectionResults class will always accept classes from, even if the classes do not qualify as cache-safe. */ static final Set<ClassLoader> acceptedClassLoaders = Collections .newSetFromMap(new ConcurrentHashMap<ClassLoader, Boolean>(16)); /** * Map keyed by Class containing CachedIntrospectionResults, strongly held. This variant is being used for cache-safe bean classes. */ static final ConcurrentMap<Class<?>, CachedIntrospectionResults> strongClassCache = new ConcurrentHashMap<Class<?>, CachedIntrospectionResults>( 64); /** * Map keyed by Class containing CachedIntrospectionResults, softly held. This variant is being used for non-cache-safe bean classes. */ static final ConcurrentMap<Class<?>, CachedIntrospectionResults> softClassCache = new ConcurrentReferenceHashMap<Class<?>, CachedIntrospectionResults>( 64); /** * Accept the given ClassLoader as cache-safe, even if its classes would not qualify as cache-safe in this CachedIntrospectionResults class. * <p> * This configuration method is only relevant in scenarios where the Spring classes reside in a 'common' ClassLoader (e.g. the system ClassLoader) whose lifecycle is not coupled to the application. In such a scenario, CachedIntrospectionResults would by default not cache any * of the application's classes, since they would create a leak in the common ClassLoader. * <p> * Any {@code acceptClassLoader} call at application startup should be paired with a {@link #clearClassLoader} call at application shutdown. * * @param classLoader * the ClassLoader to accept */ public static void acceptClassLoader(ClassLoader classLoader) { if (classLoader != null) { acceptedClassLoaders.add(classLoader); } } /** * Clear the introspection cache for the given ClassLoader, removing the introspection results for all classes underneath that ClassLoader, and removing the ClassLoader (and its children) from the acceptance list. * * @param classLoader * the ClassLoader to clear the cache for */ public static void clearClassLoader(ClassLoader classLoader) { for (Iterator<ClassLoader> it = acceptedClassLoaders.iterator(); it.hasNext();) { ClassLoader registeredLoader = it.next(); if (isUnderneathClassLoader(registeredLoader, classLoader)) { it.remove(); } } for (Iterator<Class<?>> it = strongClassCache.keySet().iterator(); it.hasNext();) { Class<?> beanClass = it.next(); if (isUnderneathClassLoader(beanClass.getClassLoader(), classLoader)) { it.remove(); } } for (Iterator<Class<?>> it = softClassCache.keySet().iterator(); it.hasNext();) { Class<?> beanClass = it.next(); if (isUnderneathClassLoader(beanClass.getClassLoader(), classLoader)) { it.remove(); } } } /** * Create CachedIntrospectionResults for the given bean class. * * @param beanClass * the bean class to analyze * @return the corresponding CachedIntrospectionResults * @throws BeansException * in case of introspection failure */ public static CachedIntrospectionResults forClass(Class<?> beanClass) throws BeansException { CachedIntrospectionResults results = strongClassCache.get(beanClass); if (results != null) { return results; } results = softClassCache.get(beanClass); if (results != null) { return results; } results = new CachedIntrospectionResults(beanClass); ConcurrentMap<Class<?>, CachedIntrospectionResults> classCacheToUse; if (ClassUtils.isCacheSafe(beanClass, CachedIntrospectionResults.class.getClassLoader()) || isClassLoaderAccepted(beanClass.getClassLoader())) { classCacheToUse = strongClassCache; } else { if (logger.isDebugEnabled()) { logger.debug( "Not strongly caching class [" + beanClass.getName() + "] because it is not cache-safe"); } classCacheToUse = softClassCache; } CachedIntrospectionResults existing = classCacheToUse.putIfAbsent(beanClass, results); return (existing != null ? existing : results); } /** * Check whether this CachedIntrospectionResults class is configured to accept the given ClassLoader. * * @param classLoader * the ClassLoader to check * @return whether the given ClassLoader is accepted * @see #acceptClassLoader */ private static boolean isClassLoaderAccepted(ClassLoader classLoader) { for (ClassLoader acceptedLoader : acceptedClassLoaders) { if (isUnderneathClassLoader(classLoader, acceptedLoader)) { return true; } } return false; } /** * Check whether the given ClassLoader is underneath the given parent, that is, whether the parent is within the candidate's hierarchy. * * @param candidate * the candidate ClassLoader to check * @param parent * the parent ClassLoader to check for */ private static boolean isUnderneathClassLoader(ClassLoader candidate, ClassLoader parent) { if (candidate == parent) { return true; } if (candidate == null) { return false; } ClassLoader classLoaderToCheck = candidate; while (classLoaderToCheck != null) { classLoaderToCheck = classLoaderToCheck.getParent(); if (classLoaderToCheck == parent) { return true; } } return false; } /** The BeanInfo object for the introspected bean class */ private final BeanInfo beanInfo; /** PropertyDescriptor objects keyed by property name String */ private final Map<String, PropertyDescriptor> propertyDescriptorCache; /** TypeDescriptor objects keyed by PropertyDescriptor */ private final ConcurrentMap<PropertyDescriptor, TypeDescriptor> typeDescriptorCache; /** * Create a new CachedIntrospectionResults instance for the given class. * * @param beanClass * the bean class to analyze * @throws BeansException * in case of introspection failure */ private CachedIntrospectionResults(Class<?> beanClass) throws BeansException { try { if (logger.isTraceEnabled()) { logger.trace("Getting BeanInfo for class [" + beanClass.getName() + "]"); } BeanInfo beanInfo = null; for (BeanInfoFactory beanInfoFactory : beanInfoFactories) { beanInfo = beanInfoFactory.getBeanInfo(beanClass); if (beanInfo != null) { break; } } if (beanInfo == null) { // If none of the factories supported the class, fall back to the default beanInfo = (shouldIntrospectorIgnoreBeaninfoClasses ? Introspector.getBeanInfo(beanClass, Introspector.IGNORE_ALL_BEANINFO) : Introspector.getBeanInfo(beanClass)); } this.beanInfo = beanInfo; if (logger.isTraceEnabled()) { logger.trace("Caching PropertyDescriptors for class [" + beanClass.getName() + "]"); } this.propertyDescriptorCache = new LinkedHashMap<String, PropertyDescriptor>(); // This call is slow so we do it once. PropertyDescriptor[] pds = this.beanInfo.getPropertyDescriptors(); for (PropertyDescriptor pd : pds) { if (Class.class.equals(beanClass) && ("classLoader".equals(pd.getName()) || "protectionDomain".equals(pd.getName()))) { // Ignore Class.getClassLoader() and getProtectionDomain() methods - nobody needs to bind to those continue; } if (logger.isTraceEnabled()) { logger.trace("Found bean property '" + pd.getName() + "'" + (pd.getPropertyType() != null ? " of type [" + pd.getPropertyType().getName() + "]" : "") + (pd.getPropertyEditorClass() != null ? "; editor [" + pd.getPropertyEditorClass().getName() + "]" : "")); } pd = buildGenericTypeAwarePropertyDescriptor(beanClass, pd); this.propertyDescriptorCache.put(pd.getName(), pd); } this.typeDescriptorCache = new ConcurrentReferenceHashMap<PropertyDescriptor, TypeDescriptor>(); } catch (IntrospectionException ex) { throw new FatalBeanException("Failed to obtain BeanInfo for class [" + beanClass.getName() + "]", ex); } } BeanInfo getBeanInfo() { return this.beanInfo; } public Class<?> getBeanClass() { return this.beanInfo.getBeanDescriptor().getBeanClass(); } public PropertyDescriptor getPropertyDescriptor(String name) { PropertyDescriptor pd = this.propertyDescriptorCache.get(name); if (pd == null && StringUtils.hasLength(name)) { // Same lenient fallback checking as in PropertyTypeDescriptor... pd = this.propertyDescriptorCache.get(name.substring(0, 1).toLowerCase() + name.substring(1)); if (pd == null) { pd = this.propertyDescriptorCache.get(name.substring(0, 1).toUpperCase() + name.substring(1)); } } return (pd == null || pd instanceof GenericTypeAwarePropertyDescriptor ? pd : buildGenericTypeAwarePropertyDescriptor(getBeanClass(), pd)); } public PropertyDescriptor[] getPropertyDescriptors() { PropertyDescriptor[] pds = new PropertyDescriptor[this.propertyDescriptorCache.size()]; int i = 0; for (PropertyDescriptor pd : this.propertyDescriptorCache.values()) { pds[i] = (pd instanceof GenericTypeAwarePropertyDescriptor ? pd : buildGenericTypeAwarePropertyDescriptor(getBeanClass(), pd)); i++; } return pds; } private PropertyDescriptor buildGenericTypeAwarePropertyDescriptor(Class<?> beanClass, PropertyDescriptor pd) { try { return new GenericTypeAwarePropertyDescriptor(beanClass, pd.getName(), pd.getReadMethod(), pd.getWriteMethod(), pd.getPropertyEditorClass()); } catch (IntrospectionException ex) { throw new FatalBeanException("Failed to re-introspect class [" + beanClass.getName() + "]", ex); } } public TypeDescriptor addTypeDescriptor(PropertyDescriptor pd, TypeDescriptor td) { TypeDescriptor existing = this.typeDescriptorCache.putIfAbsent(pd, td); return (existing != null ? existing : td); } public TypeDescriptor getTypeDescriptor(PropertyDescriptor pd) { return this.typeDescriptorCache.get(pd); } }